The present invention relates generally to torsion damping assemblies comprising two coaxial parts mounted for relative angular displacement within a predetermined range against the action of resilient means interposed chordally between the coaxial parts.
As is known such torsion damping assemblies usually comprise part of a friction clutch in particular for motor vehicles. One of the coaxial parts then comprises a friction disc adapted to be fixed for rotation with a first shaft, in practice the driving shaft, the output shaft of the engine in the case of a motor vehicle, and the other coaxial part is carried by a hub adapted to be fixed for rotation with a second shaft, in practice a driven shaft, which is the transmission input shaft in the case of a motor vehicle.
Such a torsion damping assembly provides regulated transmission of the rotational torque applied to one of the coaxial parts while rotational torque is also imparted to the other coaxial part. In other words the torsion damping assembly filters vibrations which may be generated somewhere along the kinematic chain or drive line running from the engine to the axles in the case of a motor vehicle.
One of the coaxial parts of such a torsion damping assembly usually comprises a transverse web or flange, in practice a hub web, and the other comprises at least one annular guide member or washer, and in practice two such annular guide members or washers arranged on opposite sides of the hub web and connected to each other by rivets or cross members, the associated resilient means being disposed in housings formed partly in the hub web and partly in the guide washers. Friction means are usually axially interposed between the coaxial parts for introducing a hysteresis effect in the operating characteristics of the torsion damping assembly, i.e., a difference between the torque transmitted from one coaxial part to the other for an increasing relative angular displacement of a given value compared to a decreasing relative angular displacement of the same value.
In French patent publication No. 2,370,902, an arrangement was proposed wherein a friction washer was disposed in axial contact with a guide member or a component fixed thereto, on the side of the guide member facing the hub web, and urged toward the guide member by axially acting resilient clamping means which bear axially against the same guide member or component fixed thereto. There is a sort of clamping action exerted between the guide member and the axially acting resilient clamping means.
Such an arrangement has the advantage that the axially acting resilient clamping means operate on a single friction washer and are therefore operative insofar as the friction washer is operative by rotation relative to the corresponding guide member, for example, by axial lugs on the hub web, or by radial fingers on at least one of the resilient means interposed chordally between the coaxial parts, without affecting other friction means which may be provided between the coaxial parts of the torsion damping assembly.
In the above French patent publication the axially acting resilient clamping means which are individually associated with a friction washer bear axially against the rivets or cross members interconnecting the guide members.
Although such an arrangement has been found to be satisfactory it has various drawbacks. First of all, the assembly of the guide members must be carried out in two steps: in a first step a subassembly is formed by the cross members, comprising one guide member, one friction washer and the axially acting resilient clamping means associated therewith, and in a second step, after the cross members are passed through the hub web, the cross members are assembled to the other guide members.
Now, in practice, the preliminary assembly of the subassembly in the first step is rather delicate operation partly because the assembly operation requires handling the cross members which subsequently connect the guide members to each other. It is important not to damage the free end of the connecting members so that the securement of the second guide member on the cross members may be carried out under good conditions. This has meant protective caps must be provided at the free ends of the cross members which requires additional handling operations.
This preliminary assembly of the subassembly is also rather delicate because it involves the presence of the resilient clamping means inside the space defined between the guide members and therefore the resilient clamping means must be compressed.
Further, the resilient clamping means increases the axial dimension of the subassembly, the cross members may not be standard components which are provided only for connecting guide members with the clamping of the friction disc usually associated therewith.
It may be impossible to add to a conventional torsion damping assembly the arrangement of friction washer and the particular axially acting resilient clamping means just mentioned.
Finally, since the axially acting resilient clamping means are in practice radially extending leaf spring members, another difficulty may arise owing to the possible interference between the leaf spring members and the axial lugs which may be necessary for the indexing on the hub web of the associated friction washer during relative angular displacement between the coaxial parts of the torsion damping assembly.
In French Pat. No. 1,485,244 there is provided in contact with the side of the guide member directed toward the hub web, a friction washer having special axially acting resilient clamping means and it is disposed on the other side of the guide member, i.e., on the side thereof remote from the hub web, and therefore outside the space defined by the two guide members.
The assembly of the guide members is facilitated since it does not involve the compression of the axially acting resilient clamping means, which are mounted subsequently. But it is then necessary to provide on the side of the guide member facing the hub web a special washer called a retaining washer and to interconnect it by attaching means with the axially acting resilient clamping means associated with the friction washer.
In French Pat. No. 1,485,244 the attaching means comprise a nut which is threadedly engaged with a hollow threaded fastener fixed on the retaining washer, the axially acting resilient clamping means bearing against the nut.
This arrangement has a number of drawbacks. First of all, the hollow threaded fastener is of complex construction and has a screwthread which is relatively expensive to cut. Further, the nut and threaded fastener together are of a not insubstantial axial dimension for the overall assembly. Finally, when, as is most often the case, the unit defined by the friction washer and the particular axially acting resilient clamping means is located on the side of the torsion damping assembly facing the clutch cover assembly associated therewith, there are problems to locate the unit owing to the possible interference between the nut which has a substantial radial dimension and against which the axially acting resilient clamping means bear and on the other hand the clutch release mechanism of the cover assembly which is defined by the radial fingers of a diaphragm spring.